When forming sliding parts such as gears, cams, rollers, bearings and connectors in the past, composite materials were used that were composed by dispersing a fibrous filler such as glass fibers or carbon fibers in a matrix resin.
However, when producing sliding parts using a composite material like that described above, the fibrous filler may end up being oriented in a specific direction depending on the various conditions during molding (such as the shape of the molded product, locations and number of gates provided in the mold, viscosity and fibrous filler content of the composite material, and fiber length of the fibrous filler). In this case, anisotropy appears in the mechanical strength of the sliding part, thereby leading to problems such as being oriented in a direction in which there is susceptibility to the occurrence of warping in the molded product, or a direction in which there is susceptibility to breaking or cracking when an external force is applied.
On the other hand, if the fibrous filler is made to not be oriented by adjusting the aforementioned molding conditions, although the appearance of anisotropy in the mechanical strength of sliding parts as described above can be prevented, in this case, the majority of the fibrous filler present near the sliding surface of the sliding part is facing in a direction perpendicular to the sliding surface, and since the microscopic smoothness of the sliding surface is impaired as a result of this, the coefficient of friction of the sliding surface increases, thereby leading to a decrease in sliding performance.
In addition, conventional precision parts were known to be produced by using plastic for the main plate, bridge, rotor and fifth wheel-and-pinion used in timepieces. An example of this is described in Japanese Patent No. 2962320.
However, conventional precision parts have poor transferability, and there were discrepancies between the dimensions of the injection molding mold and the dimensions of the part following injection molding. Consequently, extremely small parts were unable to be molded into highly precise shapes, and in the case of wheel-and-pinions having a small outer diameter, there was the problem of being unable to produce these parts using plastic to the excessively small curvature of the tip.
In addition, conventional precision parts lack smoothness and flatness for the surface of plastic molded products, and in the case of thermoplastic resin in particular, there was the problem of insufficient strength of the plastic molded parts.